const mySet = new Set()
const arr = [1,1,2,3,4,5,4,2,1]
arr.forEach(item => {
    mySet.add(item)
})
console.log(mySet.keys())

const myMap = new Map()
const o = {name: 'kaho'}
myMap.set(1, 'content')
myMap.set(1, 'content')
myMap.set(1, 'content')
console.log(myMap.keys())